This invention concerns wound dressings particularly as wound treatment means in the granulation and epithelization phase. These wound dressings are useful for moist treatment of wounds in particular.
The healing of skin wounds is based on the ability of the skin to regenerate epithelium and also connective and supporting tissue. Regeneration itself is characterized by a complex interplay of overlapping cellular activities which advance the healing process step by step. Three essential healing phases of a wound have been described in the literature irrespective of the type of wound. They include the inflammatory or exudative phase for blood coagulation and wound cleaning (phase 1, cleaning phase), the proliferative phase for building granulation tissue (phase 2, granulation phase) and the differentiation phase for epithelization and scar formation (phase 3, epithelization phase).
Numerous proposals for augmenting the individual wound healing phases are described in the literature. Especially wound dressings comprising hydrogels have for some time been the subject matter of numerous articles in the technical literature and also of patent documents. The European patents EP 455 324 B1, EP 528 091 B1, EP 567 704 B1 or EP 630 629 B1, for instance, describe transparent hydrogel wound dressings having various constructions. These sometimes multilayered wound dressings comprise a water-containing or dehydrated hydrogel as wound contact layer for the treatment of burn wounds.
EP0426422B1 discloses a wound dressing comprising a hydrogel based on a polyurea-polyurethane copolymer. The compositions described contain 15 to 30 wt % of a polyhydric alcohol. The ratio for reactive groups of isocyanate to amine groups in the hydrogel compositions described in EP0426422B1 is in the range from about 0.63 to 1.40. The ratio is 1.23 in an embodiment said to be preferred. A wound dressing which contains a hydrogel according to the compositions described in EP0426422B1 is on the market under the designation Hydrosorb® (Paul Hartmann AG, Germany). The wound dressing is capable of absorbing about twice its own weight of liquid within a period of 48 hours.
Furthermore, the European patents EP 457 977 B1, EP 486 522 B1, EP 541 390 B1, EP 541 391 B1, EP 570 430 B1, EP 665 856 B1, EP 691 113 B1, EP 693 913 B1 or EP 1 082 146 B1, for example, describe wound dressings having various constructions where the absorbent layer comprises a polyurethane foam.
In addition, the European patents EP 855 921 B1 and EP 1 156 838 B1 disclose wound dressings comprising a polyurethane foam coated with a hydrophobic silicone gel. This silicone gel is said to inhibit the adherence of the wound to the polyurethane foam.
Furthermore, the international applications WO 02/38 097 A1, WO 02/47 761 A1, WO 03/011 352 A1, WO 03/086 255 A1, WO 2004/052 415 A1 or EP 1 658 865 A1 describe wound dressings comprising a hydrogel and a polymer foam.
The applicant's application for patent under application number DE102008031183.9, which constitutes state of the art within the meaning of EPC Article 54(3) likewise describes a multilayered or multi-ply wound dressing having a wound contact layer as first layer and at least one second layer as absorbent layer which comprises a hydrophilic foam of polyurethane. The wound contact layer can be a hydrogel based on a polyurea-polyurethane copolymer. The operative example of DE102008031183.9 discloses a hydrogel comprising 17.5 wt % of propylene glycol, while the ratio for reactive groups of isocyanate to amine groups in the hydrogel described is 1.23. Using the polyurea-polyurethane copolymers described as wound contact layer in multilayered bandages provides atraumatic wound dressings having very good wound healing properties. A wound contact layer composed of the polyurea-polyurethane copolymers described is stable. However, a multilayered wound dressing incorporating a wound contact layer of this type has only minimal tack in respect of surrounding wound tissue. The wound dressing has to be held on the wound by hand until fixed in place by a bandage or an adhesive plaster.
State-of-the-art wound treatment requires wound dressings which speed the healing of wounds and augment the natural wound healing process. Suitable wound dressings have to combine different desirable properties. In addition to having very good skin and tissue compatibility, a wound dressing shall ensure the moist milieu which promotes wound healing, while excess liquid should be absorbed. A wound dressing shall further have atraumatic properties, i.e., the wound dressing must be removable when it needs to be changed, without damaging newly grown wound tissue. The wound contact layer here plays an outstanding part not only in respect of the desired atraumatic property but also for providing a milieu beneficial to wound healing, owing to its direct contact with the wound tissue. A moist milieu is beneficial for wound healing, although an alkaline pH, especially above pH 8, should be avoided. At the same time, excess liquid shall be transported out of the wound region and be absorbed by the wound dressing. Excess liquid or exudate can otherwise lead to maceration of the edge of the wound. Users, such as physicians or care personnel, frequently also desire in practice that a wound dressing adhere to the wound site even before it is fixed in place by a bandage or an adhesive plaster, i.e., the wound dressing shall have a certain amount of surface tack. This is desirable particularly in the case of wound dressings that are fixed to the body using a further bandaging means, such as a retaining bandage or an adhesive plaster. If the wound dressing has tack, the person applying the treatment can initially secure the wound dressing loosely on the wound and thereafter for example ready a suitable retaining bandage without at the same time having to use a hand to press down the wound dressing on the wound. A wound dressing with tack is substantially easier to use, especially when the dressing is applied by only one person. On the other hand, excessive force of adherence can lead to reducing the atraumatic property of the wound dressing and furthermore, when the dressing has to be changed, cause damage to the intact skin surrounding the wound. Excessive tack can also be less desirable because the positioning of a wound dressing which adheres too strongly to the wound tissue and to the healthy skin surrounding the wound is very difficult to correct after the first contact with the wound.